The presently disclosed subject matter relates to a TWA measuring apparatus and TWA measuring method which can accurately measure TWA (T-wave alternans).
TWA appears at onset of illness such as QT prolongation syndrome, variant angina, acute myocardial ischemia, electrolyte abnormality, paroxysmal tachycardia, bradycardia, or pericardial fluid accumulation. TWA is a phenomenon in which the amplitude and polarity of the T wave appearing in an electrocardiogram are alternately changed, and an index effective to predict sudden cardiac death. TWA is not a phenomenon which can be always observed with the naked eye, and therefore its application in clinics is limited.
From the 1980s, consequently, techniques for enabling a microvolt level of TWA (Microvolt TWA: MTWA) to be measured by a computer have been developed.
Examples of currently proposed techniques for measuring TWA are a measurement technique based on the MMA (Modified Moving Average) method of General Electric (GE) Company, and that based on the periodogram of Cambridge Heart (CH), Inc. which are disclosed in U.S. Pat. No. 6,668,189 and U.S. Pat. No. 5,935,082, respectively.
In the measurement technique of GE Company, TWA is measured from the amplitude difference of T-waves between the average waveform of odd-numbered beats (hereinafter, referred to as odd beats) and that of even-numbered beats (hereinafter, referred to as even beats). The measurement technique of GE Company is directed to a method of analyzing a waveform in a time domain, and is said to have resistance to noises. However, the technique does not have a long history as a measurement technique, and it is required to watch its clinical effect.
In the measurement technique of CH Inc., by contrast, TWA is measured by performing a spectrum analysis of an electrocardiogram derived from special electrodes. The measurement technique of CH Inc. has been used from the 1980s, and hence its effectiveness in clinics has been proved.
Today, therefore, it is considered that the measurement technique based on the periodogram of CH Inc. is clinically more useful than that based on the MMA method of GE Company.
With respect to the measurement technique based on the periodogram of CH Inc., after its announcement, various techniques for performing new processes, such as a technique of measurement electrodes are added, and still now the added latest techniques have been used.
TWA is a phenomenon in which T waves of odd and even beats are alternately changed. In the related-art technique for measuring TWA based on the periodogram disclosed in U.S. Pat. No. 5,935,082, a value (alternans voltage) indicative of the magnitude of TWA, and a value (alternans rate) indicative of the reliability of the value indicating the magnitude of TWA are calculated, and, when the magnitudes of the values are equal to or larger than predetermined values, respectively, it is determined that TWA exists.
In the related art, as described above, the presence/absence of TWA can be determined, but the states of odd and even beats cannot be sufficiently known. Moreover, it is impossible also to objectively know the reliability of the value indicating the magnitude of TWA.